German Patent No. 33 17 942 C2 describes a circuit arrangement for the protection of mechanical switchgear by an electronic switch. The mechanical switchgear assemblies are connected in series with ohmic inductive loads that are supplied with direct current. In this context, the electronic switch can be controlled by a capacitor that is charged from the load voltage. The electronic switch is connected in parallel to the load and becomes conductive when the switchgear is turned off. A non-linear resistor is connected in parallel to the electronic switch, and the parallel circuit is in turn connected in parallel to the load. The circuit arrangement operates in a manner similar to a free-wheeling diode connected in parallel to the load. As long as a control supply voltage source is connected to the load, the capacitor is charged and the electronic switch is conductive. As soon as the control voltage source is isolated from the load, the capacitor is discharged, resulting in the electronic switch becoming non-conductive. The current still flowing through the ohmic inductive load due to the stored magnetic energy is switched to the non-linear resistor by the electronic switch, resulting in a quick final decay of the residual energy stored in the inductance.
Such ohmic inductive loads include, for example, contactor coils supplied with direct current by a control supply voltage source, Depending on the size of the contactor and of the contactor coil used, decay times of 100 to 300 msec are obtained, which is still relatively slow for the requirements.
German Utility Model No. 94 09 760.7 describes a circuit arrangement for actuating a contactor. A free-wheeling branch, comprising a switching transistor and a free-wheeling diode connected in series thereto, is connected in parallel to the contactor coil. A free-wheeling controller controls the switching transistor as a function of the shape of the control voltage.
Furthermore, German Published Patent Application No. 43 21 127 describes a device for activating an electromagnetic load. This device comprises a series connection of the electromagnetic load with a first switching means, a free-wheeling circuit for the electromagnetic load, comprising a second switching means, and an actuator means for the switching means.